Out of my Head was made into a movie titled Unknown in 2011 (hence the re-publication of the book under that title), directed by Jaume Collet-Serra and starring Liam Neeson, Frank Langella, and Bruno Ganz

"The scientific gloss helps cover some of the plot's surface implausibilities. In fact, the premise is so intriguing, and so engagingly developed, that you won't mind that Martin never bothers to, say, seek out the U.S. embassy for help." - Thom Geier, Entertainment Weekly

"This is a novel that really, really wants to be a movie. There are a lot of hurried conversations on cellphones, and a lot of jumping in and out of taxis. (...) Despite all the nudging and winking and scientific showing off, van Cauwelaert's novel, in this lucid translation by Mark Polizzotti, is not without its satisfactions -- especially when it stops being literary and settles for being simply thrilling. Its surprising denouement works a retrospective magic. It explains, if it doesn't excuse, some of the flaws that came before: what looked contrived now looks cunning; what looked stylized now looks smart." - Sophie Harrison, The New York Times Book Review

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Out of my Head -- now re-published as a movie tie-in under the title they gave the film, (Unknown) --
has a promising beginning: Martin Harris is released from hospital after a brief stay following an accident that left him in a coma for a few days, but when he returns home
a man answers the door ... claiming to be Martin Harris (and wearing his pajamas).
Liz, his wife, also refuses to recognize him -- and so:

I remain frozen in the silence of the landing, with no explanation for this absurdity.
How can you prove what's obvious when everyone denies it, and you've got no proof to offer them other than your own good faith ?

An American botanist just arrived in Paris, Martin is more than a bit at a loss.
Everywhere he turns, no one can help him and few believe him.
The authorities, both American and French, are no help -- and the other Martin Harris has a valid passport, with the arrival-stamp just where they had put it when the 'real' Martin Harris arrived in the country.
The 'real' Martin has no documentation and no one able (or willing) to identify him.
Martin still has all his memories, remembering practically every detail of his life and work -- and we're talking about real detail here -- yet almost no one is convinced: "I've lost everything except my memory", he laments.
His doctor at least takes him seriously, and there's Muriel, the woman who tries to help him out, but Martin has gotten himself into a mess he can't see his way out of.
Eventually he hires a private investigator -- a "research agent" -- to gather the supporting evidence of his identity from the United States, where there should be far more of it.
And, after all, Martin can provide all sorts of details to follow up on, from his social security number to friends and colleagues who will be able to identify him from a picture.
Martin suspects it's a major agri-business that is behind all this -- Monsanto or the like, trying to make the botanist a persona truly non grata because of his research into genetically modified plants.
Rather than getting clarity -- and his identity -- things get more confusing.
The research agent's report is ... not helpful.
And then there are things like Martin suddenly finding he can play piano, despite having no memory of ever having learned it .....
How big is this conspiracy -- or Martin's delusion ?
There's a twist to Out of my Head, of course; an explanation of exactly what's going on.
It's a decent idea, but Cauwelaert has difficulty going into full thriller-mode, as the idea requires; Cauwelaert also lacks the depth to have more philosophical fun with the situation, which might also have worked.
Either way, for Out of my Head to really work he would have had to let loose considerably more, and he just can't.
The dialogue-heavy -- and confrontation-filled -- narrative has some good starts, but also jerks to too many stops, with Cauwelaert never developing that action-packed flow that real thriller writers manage.
Out of my Head has all the right pieces -- and that's why it may work quite well as a film -- but there's not nearly enough padding (or, ultimately, excitement) in the book itself.